Posted
by
timothy
on Saturday August 13, 2011 @08:18PM
from the lunch-dark-matter-doubly-so dept.

anonymousNR writes "A CERN physicist has a new theory explaining the rotational curves of galaxies. 'The key message of my paper is that dark matter may not exist and that phenomena attributed to dark matter may be explained by the gravitational polarization of the quantum vacuum,' Hajdukovic told PhysOrg.com. 'The future experiments and observations will reveal if my results are only (surprising) numerical coincidences or an embryo of a new scientific revolution.' Given the many theories around explaining various observations in recent times, there seems to be a breakthrough on its way in our understanding of the cosmos."

Agreed. I have always had a hard time stomaching the theory that dark matter and dark energy exist. It seems far too much like aether, i.e. something made up to fill a gap in knowledge without much evidence backing it up. "Look, my equations don't work out in every situation. EUREKA! If I just make some shit up like say, invisible matter that doesn't interact with other matter except through gravity, I can make my equations work!". I think its probably that the equations are based on more special cases. Thi

I will admit its not totally unfeasible. I have to if I am to be intellectually honest. However, to me it seems like a taller order to prove there are these particles than to just assume the model doesn't fit every situation since its not complete and does not adjust itself to every situation. Their could be an infinite amount of other explanations for the phenomena rather than just inventing some particle. As a matter of fact, Godel proved that no finite set of axioms can capture all of mathematical truth.

I'm no cosmologist, but my understand is that there IS direct evidence of dark matter [universetoday.com] - in the way galaxies collide. Normal matter collides because it interacts through EM and hence slows down, while dark matter doesn't and doesn't. This can be seen by comparing X-ray imaging to map the normal matter and gravitational lensing to map the dark matter.

I've heard the "irreducible complexity" arguments before - the one that closet creationists such as Michael Behe thought they could beat the evolutionary forces over the head with was the bacterial flagellum. It was very widely used and probably still is by the ones who refuse to read biology texts.

But, it was refuted years ago, probably not long after Behe started preaching it.Ken Miller does a long, thorough talk on refuting the bacterial flagellum - it's a bit long but very informative, if you have an o

Dark matter has the same feel to it, but I am not a physicist. And some types of dark matter are observed aka neutrinos.
If free neutrons didn't have such a short decay time, I'd consider that option as well. Without electrons the photon interaction with a neutron seems considerably hindered but again I'm not a physicist.

Neutrinos are too light to be Dark Matter. Their low mass means that they are produced moving at almost the speed of light so, if they were the Dark Matter, the "wrinkles" we see in the Cosmic Microwave Background would be far more blurred out than they are.

If free neutrons didn't have such a short decay time, I'd consider that option as well.

Sorry but neutrons interact via the strong nuclear force and so cannot be dark matter otherwise we would see it interacting with atomic nuclei.

Without electrons the photon interaction with a neutron seems considerably hindered

Electrons have nothing to do with photon interactions with neutrons. Neutrons are made of quarks so photons of sufficient energy can directly interact. Electrons can interact with neutrons either via EM (photon) or weak nuclear interactions.

"Look, my equations don't work out in every situation. EUREKA! If I just make some shit up like say, invisible matter that doesn't interact with other matter except through gravity, I can make my equations work!"

It's a little more complicated than that..

It's hard for a theory to get an overwhelming majority of scientific opinion without it being pretty solid, and it's much easier to say you think something is wrong than to substitute it for something better.
("The models imply matter we can't observe directly, but that can't be! EUREKA! I'll just change the model so that it behaves as if the invisible matter was there even though it actually isn't! How non-kludgy and elegant!")

I have always had a hard time stomaching the theory that dark matter and dark energy exist.

It was never a theory. Based on a number of different observations, physicists could not account for matter and energy that appear to be missing from our observable universe. It was only called dark matter and energy because there was no other way to describe. Based on other determinations, this energy and matter would have weird properties if it existed. Scientists have never actually said it existence but only it might exist. If they could account for this gap of observations due to empirical error, they would embrace it but different aspects of observations suggest that the gap is not easily explained. So right now the focus is on explaining the gap.

Think of the difference between Newtonian and Relativistic models.

I think you mean the difference between quantum theory and relativity. Relativity encompasses Newton's models for gravity.

The luminiferous aether is a substance that was invented to explain something that seemed missing from our theories (specifically, what it is that the speed of electromagnetic waves given by Maxwell's Equations is relative to). It made predictions, those predictions were tested, and so the idea was tossed out.

Dark Matter is a substance that was explained something that seemed missing from galaxies and clusters of galaxies (specifically, there wasn't enough mass there to explain why they held together given how fast things were moving). The idea of Dark Matter made predictions, those predictions were tested, and they *confirmed* Dark Matter.

There's nothing magic about Dark Matter. And the lines of evidence are more than just some equations that don't balance out.

Agreed. I have always had a hard time stomaching the theory that dark matter and dark energy exist. It seems far too much like aether, i.e. something made up to fill a gap in knowledge without much evidence backing it up.

The problem is that the universe is pretty good at ignoring people's bowel movements, a lot of things are completely unintuitive. If I look at a wall it looks damn solid to me, my gut feeling would be that radio and wireless can't possibly work. And if you told me there are particles that'll pass through thousands of miles of earth and stone and lava without even caring that it's there, I'd say you were ready for a room with padded walls if only it wasn't true. In short, past experience has shown us that this is an area where the universe has a habit of not acting the way people expect.

That said, we do know our understanding of gravity is incomplete at the quantum level, we probably will get a better understanding of it as we go along. But the unexplained gravitational effect seems variable, lumped together just like real matter and not always directly in proportion to it. I could accept that we might have had to adjust gravity by some sort of factor but it seems a bit too erratic to be just a formula adjustment. I at least am pretty confident that we've not found all the particles yet and that this will be at least part of the explanation.

Go to a fundamentalist church group some time and tell me you really think they are more capable of understanding when they are wrong.

Would you want someone to base their opinion of Americans based on trip to a US insane asylum? If not then why would you think a visit to a fundamentalist church would be a good way to judge a religion as a whole? Both are only fractions of their respective societies and both are filled with people who have a tenuous grasp on reality. It is bad science to use a biased sample like that on which to base your judgements.

The difference is that scientists embrace the whole idea of proving themselves wrong, and are willing to walk away from obviously nonsensical explanations for things. Religious people instst on sticking with their obviously nonsensical explanations, and all of the hideous moral baggage that goes with doing so.

The difference is that scientists embrace the whole idea of proving themselves wrong, and are willing to walk away from obviously nonsensical explanations for things.

I think you have a pretty naive view of scientists. You really think ALL people who built a career based on a theory are just willing to say "oops" and let their work and reputation become irrelevant? Sure, there are many scientists who are noble enough to do so. But when you look at the history of science, even recently, there are many popular but disproved ideas that stick around for decades, even longer... until people die off or retire, or until the evidence against them becomes so strong that people

Uhh, well. Scientists never actually claim to "know" the truth about anything completely, they just claim to know "an approximation of the truth" which is a theory or axiom that has been tested and shown to work in every case its been tested in so far. People still continue to test it and find it works. GPS satellites would not work if Relativity was not mostly correct. Don't get confused with the word "approximation of truth", it doesn't mean its not correct to a degree. There is no absolute right and absolute wrong.

The principal of science is that you seek truth through observable, repeatable experiments. We know gravity exists on Earth because every time we throw a rock in the air it falls back to the ground. If one day, it did not fall back to the ground, or it fell to the ground 50 percent of the time and the other 50 percent of the time it flew off into space; we would probably not believe gravity existed and instead either have worked on or be working on other explanations. For example, Relativity has passed just about every test its been put through except for things on quantum scale or on super-massive scale. Does this mean it is wrong? No. It means that it is right in certain situations, but not in others. If you know anything about mathematics, which is totally based in rigorously proved logic that is basically irrefutable once its axioms and assumptions are cemented, you will realize that sometimes its possible to be correct within a certain degree or domain but incorrect beyond it.

Its a bit different to claim many of the things religions claim. For example, claiming a flood wiped out all humans on Earth except for Noah, his sons, and all of their spouses along with two of each animal is ludicrous. The fossil record shows absolutely no evidence of this and a global flood poses other physical questions that have completely unfeasible explanations, and its been proven so if you actually read about scientific topics such as genetics, biology, anthropology, paleontology, and physics/geophysics/meteorology (particularly atmospheric pressure). They don't specifically say that the flood didn't happen, nor do they attack it. They just show certain timelines for fossils, or certain geological strata or certain physical relationships (in the form of equations) that make something like a global flood seem ridiculous. Maybe it happened on a smaller scale, but your will find its absurd to think it happened over the whole earth.

You see, religions claim to "know" things and require absolutely no proof at all other than faith; which is belief without evidence. They won't admit when they are wrong even in the face of overwhelming evidence against their belief. That's not to say scientists don't believe things too and sometimes be stubborn about changing them, its just that religions don't believe things based on logic and evidence whatsoever. Even scientists are humans, and make errors sometimes. However, their training helps them remove illogical or absurd things from their minds rather than hold on to them when overwhelming evidence is put in their face. I don't think that religious fanatics are incapable of being as smart as scientists, I just think many of them are brainwashed or undereducated.

Does all of this mean God doesn't exist? No. Its just that there is no evidence of them existing, nor is there necessarily a reason they must exist. I for one am not sure. I admit it is possible, but I have not seen evidence to support it nor do I see a theory that holds up when tested that shows there must be one. Some people choose to believe there is no God, some people believe there probably is, and some people simply don't know. Whatever you believe is what you believe, but please don't assume that scientists are out to get you, or make you change, or disprove god. By definition the existence of God couldn't be proved anyway, since even if we "found God", how do you know its not just a super-advanced alien being? Even if their is an afterlife you won't truly know if God exists because for all yo

Science still requires a "leap of faith" if you will, but it's entirely different from that of religion. Namely, science is, at it's core it is a system of observations and predictions, with a framework that allows others verify those predictions given the same observations. How well it models "reality" is a separate, and ultimately philosophical, issue. To put it (overly) concisely, there is a branch of philosophy that states that we cannot truly "know" anything because we can only learn things through

No one would have a problem with the notion of such a God. It's when the God of all space and time starts setting bushes on fire and demanding that people vote Republican that people start to call bullshit.

What if I was to posit that what we call "God" is actually the universe itself and that life is an attempt by the universe to understand itself, using reason, in the brief period that life can exist before the universe subsequently decays into entropy.

You're free to do that if you want, we really can't stop you.

However, after that point, when you tell someone "I believe God exists", they will not have the faintest clue what you're talking about - they'll think you're talking about the usual definition of Go

Well, actually, in a way, Dark matter is "Hell, I don't know". It's just that it's a bunch of "Hell, I don't know" that fills certain holes in a theory. I'd list all the things that we now understand (better than we did, at least) that were once just "Hell, I don't know" fitting into a hole in a theory, except that I want to finish this post some time this year.

I've long thought that the concept of dark matter was a manifestation of the inability of some scientists to admit "Hell, I don't know".

..what? Dark matter is, by definition, little bits of "hell, I don't know". Fuck, we don't even know if it's bits or bobs or particles or globs! We have no idea what it is at all!

I mean, why do you think we call it "dark matter"? That is literally all we know about it - we know it has weak electromagnetic interactions (i.e, it's dark), but strong gravitational interactions (i.e, it's matter).

The thing you really seem to object to is that scientists will say "Hell, I don't know - but I'll put a name on it, and start narrowing down what it can and cannot be".

I mean, what do you expect? That we'll admit "hell, I don't know" and just stop? And just give up right there? Hell no - saying "I don't know" is the first step of doing science, not the last step!

I'd love to see how his model explains something like (e.g) the Bullet Cluster [wikipedia.org], because quite frankly I don't think it does - the article states that his theory explains the speeding up of galactic rotation (the reason why we first hypothesized dark matter), but the article goes on to state that his hypothesis doesn't actually cover a ton of other stuff like the CMB.

Furthermore, this theory is based on the hypothesis that matter and antimatter are gravitationally repulsive, which (imo) is absolute BS. It's true, we haven't generated enough antimatter yet to know for a fact that it acts the same way as regular matter in a gravitational field generated by regular matter, but we have absolutely no reason to think that it would be gravitationally repulsive. If that turns out to be true, there will need to be a shit-ton of rejiggering of models and basically everything we think we know about physics will have to be moved around.

Basically, he's said "If pigs can levitate, then I can account for the discrepancy in galactic rotation curves without dark matter" - except if pigs can levitate, we'll need to rethink everything anyway.

Yay for phlogiston [wikipedia.org] and aether [wikipedia.org]. Dark matter might end up on the list of ideas that physcists turned to in order to explain things that had other explanations. La plus ca change...

>>Yay for phlogiston and aether. Dark matter might end up on the list of ideas that physcists turned to in order to explain things that had other explanations. La plus ca change...

And yet we're back to something like aether with relativity and string theory. Relativity says that empty space has a structure, and string theory says empty space is made up of a lattice of vibrating strings that propagates everything in the universe.

Not exactly. At least we can predict certain behaviors using Relativity that enable satellites to work properly as well as a whole slew of other physical behaviors that enable our modern technology to work. If we didn't adjust GPS satellites using relativity they would not work at all. I would wager similar usefulness did not come out of the theory of aether but I am willing to admit I am wrong if you can present evidence to the contrary.

Hopefully. Dark matter is a very inelegant solution to observations that don't agree with theory. Even so, working out what properties it must have, should it exist, is a useful exercise because it clarifies the problem more thoroughly.

There seems to be a common misconception that incorrect theories were stupid ideas from the get-go. That's really not the case, until new evidence or new ideas come up the incorrect theories are every bit as valid as the ones that may turn out to be correct and the differences between the various competing theories may point the way to interesting new experiments.

This new theory is probably wrong, but it's founded on an assumption that, while not currently accepted as true, is experimentally verifiable. That's the assumption that anti-matter and matter have gravitation fields of opposite sign. An experiment to determined the truth of that would be very interesting.

Exactly. It was the development of the theory of the aether that led to many of the experiments surrounding the properties of light that allowed the theory of relativity to be developed. For instance, we knew if aether existed it would create a "wind" that would slow light in some directions as the earth moved. The experiment to test that wind helped found the theory of relativity (although, interestingly enough, Einstein supposedly hadn't heard of the experiment when he postulated the constancy of the speed of light.)

Aether was by no means a stupid theory, but it required a number of new properties previously unseen in material bodies, and it was theorized solely as a kludge to explain the motion of light through a vacuum. The analogy with dark matter is quite strong. Dark matter, too, has never been observed, and possesses properties of matter previous unseen or indeed thought impossible, and exists solely to bridge a gap between our model of how things should behave, and how things actually behave. This does not bode well for it. However, the experiment to test for its existence is quite likely to lead to something interesting, even if we have no idea what.

Dark matter might end up on the list of ideas that physcists turned to in order to explain things that had other explanations.

What really surprises me is, despite this, so many physicists have jumped on the bandwagon. Average Slashdotters have been more skeptical of they dark matter theory than physicists, from what I've seen.

"It's invisible, we have no idea what it looks like, we can't detect it, but it must be there because we have no other ideas." Exactly the same mistake as the theories you point out.

But it doesn't fit the data -- the dark matter theory is constantly being revised. First it's "90%" of the mass of the universe, then it's "70%", then we're back to "98%", then there's dark energy, then the fractions change again, and again, and again.

That's not a fit! It's not like we started at, say, 80%, then refined the fit to 82.5%, then an additional data helped us narrow it down to 82.515%, and so on. It's just jumping all over the place.

Secondly, it's not "fitting to the data", it's fitting to the difference between a theory and the data. There's a huge difference. And it's particularly galling that the "theory" used is Newtonian gravity, when it's been known to be wrong for a century! Several papers have been released that show that it's possible to make the need for dark matter vanish by using relativistic mechanics. Not exactly surprising that the "difference" is affected by the theory chosen!

Every research paper about dark matter reads something like "we use a simplified theory of gravity because of [excuse], and then oh look, we find that our hugely simplified model doesn't agree with observations, so clearly there's an invisible something out there". The excuses vary between: "The other paper did it too", "Relativistic equations are hard, and I'm lazy", "I don't understand relativity so I don't know how it could possibly apply to galaxy sized masses thousands of light years in size", and "my computer is too slow to do this properly".

This is because average Slashdotters do not have even the beginnings of a clue about astrophysics

Yeah, well, I studied Physics at a university level, and I think dark matter smacks of hubris, laziness, and weak logic. It sounds an awful lot like chasing the error terms in Epicycles [wikipedia.org] a century too late.

The latest attempts to explain dark matter are an ever bigger joke, like Modified Newtonian dynamics [wikipedia.org]. Here's a hint... we already have a "modified" theory for motion -- it's called relativistic dynamics!

Until some physicist demonstrates that dark matter is still required to explain measurements when the theory used is the full general relativistic model with speed of light delay included, I'm just going to automatically assume that dark matter is bullshit.

This kind of thinking is all too common in Physics. A classic example is the double-slit experiment [wikipedia.org]. Every textbook states a formula for the spacing of the interference fringes that disregards a bunch of things, handwaving them away as "unimportant". A math-geek friend of mine in my physics class was upset by this lack of rigor, walked up to the whiteboard, and demonstrated that the simplifications can result in errors as large as ten percent or more in real-world scenarios!

Imagine someone basing a new theory of light based on the difference between observed interference fringe spacing and the simplified theory. That would be stupid, wouldn't it? Why is it then acceptable for gravity?

How can you possibly not know about the Bullet Cluster? [wikipedia.org] That is pretty much blatant evidence that there appears to be something there which is both dark and massive. Wouldn't a theory of dark matter be appropriate when presented with such evidence? (and, by the way, structures like the Bullet Cluster were predicted by the theory of dark matter - people said "well if it doesn't interact electromagnetically, we should be able to see places where normal matter got pushed but dark matter didn't, like when two clusters collide" - so they set out to look for something like that, and lo and behold they found it!)

And that's not even going in to the other things that dark matter predicts and nothing else does, like the Cosmic Microwave Background.

Or you could just read Starts with a Bang [scienceblogs.com], Ethan Siegel is a lot better at explaining this stuff than Slashdot is.

But it doesn't fit the data -- the dark matter theory is constantly being revised. First it's "90%" of the mass of the universe, then it's "70%", then we're back to "98%", then there's dark energy, then the fractions change again, and again, and again.

About the changing numbers, I'd like to see citations.

Dark energy is a completely different concept than dark matter, completely independent of it, and used to explain completely different phenomena. The only thing dark matter and dark energy have in common is

Of course, the theory is not complete, and there should be further experimental confirmation, but it looks pretty good for now.

This kind of thinking is all too common in Physics. A classic example is the double-slit experiment [wikipedia.org]. Every textbook states a formula for the spacing of the interference fringes that disregards a bunch of things, handwaving them away as "unimportant". A math-geek friend of mine in my physics class was upset by this lack of rigor, walked up to the whiteboard, and demonstrated that the simplifications can result in errors as large as ten percent or more in real-world scenarios!

Imagine someone basing a new theory of light based on the difference between observed interference fringe spacing and the simplified theory. That would be stupid, wouldn't it? Why is it then acceptable for gravity?

Well, I work in optics, and I have no clue what you are talking about here... Is it because the usual derivation uses tan(alpha) ~ sin(alpha) ~ alpha? Or because it disregards the polarization of light? I can assure you that both of those approximations are very good "in most cases". But that doesn't mean you can't use the correct formulas, if needed. More likely, your teacher was oversimplifying the problem to get accross the most important concepts without his students being drowned by little details.

But much, much more importantly, physicists know that arriving to the simplest model that explains all your experimental data is very important, because it lets you understand what's going on, instead of just making blind calculations. I can assure you that this is not an easy skill to learn, specially for math-loving students who are irritated by approximations (I know this from first-hand experience!).

So what's your idea? Given that the observed behaviour of the universe is inconsistent with what we expect, there are basically two possibilities:

1) Our understanding of gravity is wrong.2) Our understanding of the matter in the universe is wrong.

Despite lots of effort, nobody has come up with a satisfactory theory of gravity which fixes the problem. And a new theory to fix the problem is not really more satisfactory in itself than a new type of matter - they both would be fudges to fit the data until some

They've "jumped on the bandwagon" so to speak, because General Relativity explains everything else really fucking well, so we have a choice when we observe the anomalies; rewrite the entire rulebook, except we don't know how to, or postulate some form of matter that isn't *directly* observable (you know, sort of how like electrons aren't directly observable), and try to explain what it is. Maybe the latter is a fool's errand, but to throw out one of the most successful theories in history because the large

Well, that's how science works. You take a theory and as long as you have more things in favor of it than contradicting things, it has merit, at least until you have a better theory with fewer (or no) contradiction that explains nature better.

But looking at the two examples you present, maybe we should be more open minded when approaching science in general. I'm pretty sure both, phlogiston and aether, caused a lot of people to research into the wrong direction because they were considered solid theories. S

IIRC, phlogiston was one of the theories that lead to the atomic theory. In fact I seem to recall the Priestly (Lavoisier?) first called Oxygen "de-phlogistonated air" or some such. It was wrong, but a vital step along the way to a better theory.

Not exactly. The article states that physicists assume a positive charge for gravity throughout the universe. Hajdukovic, the guy that wrote the paper (I think), suggests that a negative charge exists, just like with electromagnetism. He suggests that matter produces positive gravity, and antimatter produces negative gravity. Here is an excerpt from http://www.physorg.com/news/2011-08-dark-illusion-quantum-vacuum.html [physorg.com] that explains it better than I.:

If matter and antimatter are gravitationally repulsive, then it would mean that the virtual particle-antiparticle pairs that exist for a limited time in the quantum vacuum are “gravitational dipoles.” That is, each pair forms a system in which the virtual particle has a positive gravitational charge, while the virtual antiparticle has a negative gravitational charge. In this scenario, the quantum vacuum contains many virtual gravitational dipoles, taking the form of a dipolar fluid.

“We can consider our universe as a union of two mutually interacting entities,” Hajdukovic said. “The first entity is our ‘normal’ matter (hence we do not assume the existence of dark matter and dark energy), immersed in the second entity, the quantum vacuum, considered as a sea of different kinds of virtual dipoles, including gravitational dipoles.”

He goes on to explain that the virtual gravitational dipoles in the quantum vacuum can be gravitationally polarized by the baryonic matter in nearby massive stars and galaxies. When the virtual dipoles align, they produce an additional gravitational field that can combine with the gravitational field produced by stars and galaxies. As such, the gravitationally polarized quantum vacuum could produce the same “speeding up” effect on the rotational curves of galaxies as either hypothetical dark matter or a modified law of gravity.

I have trouble figuring out why the quantum vacuum doesn't produce real rather than virtual particles, since with negative gravitational charge the net energy of a real particle pair is nearly zero

I don't really get you here. As I understand it the quantum vacuum produces anti+normal particle pairs which annihilate more or less straight away. They are there and real but they add up to nothing. If quantum vacuum produced real particles that would mean a miss-match between normal and anti particles so matter would continually appear out of nothing (hey, are you Fred Hoyle?) but that violates conservation of mass energy.

He gives an example of a dielectric slab being inserted into a parallel plate capacitor, which results in a decrease in the electric field between the plates. The decrease is due to the fact that the electric charges of opposite sign attract each other. But if the electric charges of opposite sign were repulsive instead of attractive, then the electric field would increase. Back to the quantum vacuum scenario, since the gravitational charges of opposite sign are repulsive, the strength of the gravitational field increases.

If the gravitational charge of opposite signs are repulsive, it would mean that the "vacuum gravitational dipole" will have a tendency to separate into matter and antimatter.As the antimatter is repulsed by the normal matter, wouldn't this require the introduction of another force (the "dark force"?) – that should be even stronger than the strong force – to explain how come we are not seeing flows of antimatter originating from the core of the galaxies?

Electromagnetism is stronger than gravity. Given that the particles in question also have the opposite charge, and are therefore attracted electromagnetically, it wouldn't make a major difference to them.

As the antimatter is repulsed by the normal matter, wouldn't this require the introduction of another force (the "dark force"?) – that should be even stronger than the strong force – to explain how come we are not seeing flows of antimatter originating from the core of the galaxies?

...and I say "bounce the graviton particle beamoff the main deflector dish"That's the way we do things, ladsJust making shit up as we wishThe Klingons and the Romulanspose no threat to us'Cause if we find we're in a bindWe'll just make some shit up.
-- Voltaire, "The USS Make Shit Up"

I realize this isn't a group of physicists here, but most of the arguments people here are positing against dark matter more or less boil down to "it's unintuitive". Seriously, welcome to modern physics guys.

This new idea may be the start of something (and I must say this guy certainly doesn't lack in the self-esteem department), or it may fall apart as it fails to get further developed. But until it - or another alternative idea - gain some traction with the scientific community, it's a bit premature to start writing off dark matter. At the moment, it's the best solution we've got.

Yeah I know exactly what you mean. I get this all the time from my non-physicists friends, they seem to be the most skeptical not the actual working physicists and astronomers.

You know, there's a whole class of particles, called supersymmetric particles, that most extensions to the Standard Model practically *beg* to exist, so it's not such a stretch to think that dark matter might be these one of these stable, neutral massive SUSY particles that only interact through gravity and the weak force.

Well, there's also a lot of:You're assuming that 90% of the universe is invisible on the basis of *what* evidence? I'd like a bit of better evidence, please, before I swallow something like that.

It's something that *could* be true, but the evidence is pretty thin for the size of the hypothesis. Maybe it's the best we can do, and maybe it isn't. For a while longer I'm going to presume that eventually we'll come up with either a better answer, or more convincing evidence. The current evidence is proof of

The first one can be somewhat explained by MOND. But MOND can't really explain gravitational lensing (duh, it's Modified _Newtonian_ mechanics) and it is totally busted by 3) and 4). Vacuum polarization is MOND-like in this regard and probably can't explain them as well.

Actually, the relationship between the amount of dark matter and normal matter in small galaxies is quite interesting. Unlike rotational curves and lensing it has an explanation that has nothing to do with gravitational properties of dark matter. Small galaxies have fairly shallow gravitational wells, so normal matter can be blown away by stellar winds and supernovae explosions. And since dark matter does not interact [much] with the normal matter, it tends to stay. Here's a nice overview: http://scienceblogs.com/startswithabang/2011/08/the_smallest_mini-galaxy_in_th.php [scienceblogs.com]

Well, there's also a lot of:You're assuming that 90% of the universe is invisible on the basis of *what* evidence? I'd like a bit of better evidence, please, before I swallow something like that.

There is lots of evidence. Look up "Bullet Cluster" on the net for the closest thing to a single "smoking gun". Or, for a mention of the Bullet Cluster and lots of other evidence (and not even all of it), watch this: http://vimeo.com/4559703 [vimeo.com]

From TFP: "Let us end by pointing that the rotational curves of galaxies are not the only phenomenonwhich is currently explained by Dark Matter. For instance, CMB data are apparently in favor ofthe presence of dark matter as a key for understanding of density fluctuations and the structureformation in the Universe (see review of Einasto, 2010). While our Letter gives indices that thegravitational vacuum polarization could be an alternative to dark matter in the explanation of thegalactic rotational curves,

I'm not going to actually read the paper because i have a headache already, and i'm not saying that this guy isn't onto something, but if I had an 'automatic scientific paper generator', 'gravitational polarization of the quantum vacuum' is exactly the sort of phrase it would be likely to spit out:)

Disclaimer: I'm a lay person when it comes to things like quantum physics.

From my understanding of the arguments and analogies given in the article, the explanation is that vacuum does has a digravitational constant (the gravitational equivalent of the dielectric constant) greater than 1 in strong gravitational fields.

But, by the same quantum fluctuations getting polarized argument, shouldn't vacuum also have a dielectric constant greater than 1 in strong electrical fields?

Can't we test that last hypothesis pretty easily? Is it already known?

The crux of the article's hypothesis, that anti-matter has opposite-sign gravity, seems like an attractive idea and one that should also be easily testable once sufficient anti-matter can be manufactured and contained.

if something "comes and goes" on a quantum level, faster than the universe can usefully notice, and it doesn't violate any of the "conservation (energy, momentum, information (maybe),...) laws", then it is permitted. In this case, if a positron/electron pair are spontaneously emitted from "empty" space, very, very quickly their opposite charge will attract them to each other and they will annihilate each other paying back the energy that it took to create them, so there's no "law" violated

> if something "comes and goes" on a quantum level, faster than the universe can usefully notice,

That's a relatively good explanation but I would change "faster than the universe can usefully notice" to "because the physical universe/reality is digital (Time & Space have been quantized) then something can exists at a higher frequency and not break any physical laws."

Fenyman hinted at this when he said there really is only 1 particle. It is moving so fast that it only spends a fraction of its "lifetim

Erm... gravity, as well as electromagnetism, decreases with the square of the distance. I would consider this a strong pointer to both being limited to three dimensions, as it is consistent with distributing the field over the surface of an sphere (for example).

You can detect dark matter. If it exists, we have already indirectly detected it. We have not yet directly detected it, but that is not because it not possible to do so, just that we have not succeeded yet. We are currently trying to do so.

You can detect dark matter. If it exists, we have already indirectly detected it. We have not yet directly detected it, but that is not because it not possible to do so, just that we have not succeeded yet. We are currently trying to do so.

Using similar methods, there was a time when you could "detect" epicycles, too. Like dark matter they were a theoretical fudge factor designed to prevent a cherished theory from falling apart due to its lack of successful predictions and explanatory power. In the case of epicycles, the cherished theory was geocentrism. You would have been ridiculed extensively (and quite possibly be in danger of the Inquisition) for questioning it, not because your own theory wasn't viable or couldn't also explain the observed results but because "everybody knew" how "well-established it is" that the earth is the center of the solar system...

If they teach scientists about the history of these things as part of their normal training, they don't do a very good job. At all.

Using similar methods, there was a time when you could "detect" epicycles, too. Like dark matter they were a theoretical fudge factor designed to prevent a cherished theory from falling apart due to its lack of successful predictions and explanatory power. In the case of epicycles, the cherished theory was geocentrism.

Not to be too pedantic, but the history is more complicated than that. The "cherished theory" in this case also depended on other assumptions that led to epicycles, perhaps the most notable being circular orbits.

In case you didn't know, Copernicus's theory contained a lot of epicycles too. It wasn't that much less complex than the Ptolemaic theory, despite being heliocentric. Why? Because he assumed circular orbits. It wasn't until Kepler came along with his ellipses that the epicycles disappeared.

Huh. Funny. I must have skimmed past the "EU theory" line when I read that the first time. I read the first sentence and it seemed pretty obvious that the poster was a fan of so called "Plasma Cosmology". As it happens, I do live in the US, but I'm not actually a US citizen, I didn't grow up here. Anyway, perhaps I'm ignorant, but if you could enlighten me, I would appreciate it. What exactly is European Union theory?:)